Many sports are competitive in nature, and therefore, those who participate in competitive sports typically hide their play calling from opposing teams. Secret play calling in competitive sports typically involves a play caller and a messenger. Usually the play caller is the coach and the messenger is a player. In this scheme, the coach can tell the messenger the play and the messenger subsequently reveals the secret play to teammates during play. For example, a football coach may send a substitute player out to the team huddle to reveal the secret play to the team. However, secret play calling has traditionally been prone to attenuation error and miscommunication. Like the youthful game of telephone in which an initial message loses semantic meaning as the message gets quietly passed from one child to the next, the traditional coach-messenger paradigm suffers from lose of meaning and interpretation inaccuracies.
To deal with the problems of traditional coach-messenger secret play calling, other schemes have evolved. For instance, instead of sending in named plays, the coach can device a coded system that matches each play to a unique code. In this scheme, the coach or a player could announce the code of any particular play to all members of the team. Moreover, the code could be announced loudly for anyone to hear, but the play would remain a secret that could only be deciphered by a person who understands the coach's code system. Instead of yelling out coded plays, a coach could alternatively (or in conjunction with vocalizing the coded play) display a sign with the code for the play. By holding up the sign, the players on the team would be able to see the code and thereby execute the associated play. However, like the coach-messenger play calling scheme, the coded play calling schemes (i.e., vocalizing play codes and/or displaying play codes on signs) to date have suffered a number of drawbacks. Specifically, calling plays by vocalizing (e.g., yelling) play codes depends on the hearing ability of each player and the level of background and/or ambient noise in the vicinity of the play calling. For example, some players may have general difficulty hearing while other players have trouble hearing because of equipment they use during play (e.g., a football helmet might block part or all of a player's ears). Also, crowd noise is a well-known issue that daunts even the most talented players. For instance, opposing teams playing in a domed football stadium typically suffer communication breakdowns due to crowd noise.
In addition, all of the existing schemes for calling plays are slow. It typically takes time for the coach to tell a substitute player which play the team should execute, time for the player to run out onto the field and inform the other players about the play, and finally execute the play. Likewise, it takes time for a coach to select a play to call, write a code for the play on a visible sign, and then hold up the sign in the line of sight of each player. In these play calling schemes, for example, the time involved for calling the play, conveying the play call to the team, and finally executing the play might be in the range of 20-35 seconds. This often leaves a small margin for correcting errors (e.g., football typically permits 45 seconds for a play to be called).
Thus, what is needed is the ability from the sideline to quickly call plays that only certain players can understand and whose accuracy does not break down during communication.